NOAA Teacher at Sea
Onboard NOAA Ship Oscar Elton Sette
May 2 – 25, 2004
Mission: Swordfish Assessment Survey
Geographical Area: Hawaiian Islands
Date: May 14, 2004
Lat: 18 40 N
Long: 158 14 W
Sky: Sunnny with widely scattered cumulus
Air temp: 26.4 C
Wind: 172 degrees at 12 knots
Relative humidity: 61.4%
Sea temp: 26.4 C
Depth: 888.5 m
Sea: A few white caps out there; swells in 1-3 foot range — easy going today.
Science and Technology Log
A fairly exciting morning on the longline. Several escolar, a barracuda, and a pomfret (a laterally flattened fish about 30cm long but only 2-3 cm in width with a fine set of sharp teeth). Samples taken from all. We also had a blue shark from which samples were taken and an oceanic white tip shark which was tagged and released. I got to wrestle both. Picked up a few remoras from the sharks. We think we have at least two species of remoras.
This afternoon we passed over Cross Seamount and traversed it several times as we trolled but to no avail. There will be no longline set tonight since we have a date in Kona to drop off one of the current scientific party.
I want to fill in with more of the vision story this evening if I can stay coherent long enough to convey it sensibly. I will touch on the work of Steven, Kerstin, and Rickard.
I have been collecting samples of fish lenses. They vary in size, as you would expect, among different sized fishes. What makes the lenses different from those of most vertebrates is that they are spherical rather than oval in cross section. The cornea of fish is also optically non-functional. Since it has the same refractive index as water, focusing is done by moving the lens back and forth in the eye rather than by changing the shape of the lens as our eye muscles do.
Steven uses laser light to determine the focal point for different colors of light. He suspends lenses in a fluid medium then turns on a laser beam that makes two vertical passes through the diameter of the lens. You can watch light’s path change as the beam migrates. Computer analysis then determines focal point.
Kerstin and Rickard must have live cells from the retina for their studies. Among other things, they are looking at the sensitivity of these cells to different light intensities. Live retina cells convert light to electrical signals which travel via the optical nerve to the brain to produce an image. By attaching electrodes to tissue samples about 1 cm square in size and subjecting the cells to different intensities of light electrical responses of different strengths can be detected and measured. They appear as a wave pattern on a screen. As light intensity is increased, the amplitude of the wave pattern increases. So a flat line (no response) becomes one with small amplitude waves which grow as light intensity increases to a point where more light produces no greater effect.
Lets compare two species, mahi mahi, which stay nearer well lit surface and bigeye tuna which like deeper environs. Which eye would you expect to be more light sensitive? The bigeye. Their cells are stimulated by much lower intensities of light than the mahi’s. They (bigeye) have to be able to detect their prey under minimal light conditions and need the more sensitive eye to do that. Big eyes, big pupils (fish pupil size is fixed) and a “super” sensitive set of retinal cells are adaptations of these fish to their deep environment.
I’ve had enough (as I suppose you have too). I will wrap up the vision story tomorrow or Sunday.
We are headed for Kona. Although we probably will not get any shore time, it has been suggested that there might be an excursion to a place where we can swim/snorkel for awhile. I am hoping very much this it true as are others. A plunge into this element (I guess I should say compound) that we have bobbed around on top of for the past 13 days would be a pleasant change in the routine and scenery.
Reading E.O. Wilson’s The Diversity of Life.
I would like to thank, Ron, a fellow teacher from Michigan who I have never met, for writing a note to tell me that he has been enjoying the logs and also to pose a question. Much appreciated!
Sunrise here today is at 6AM and the great yellow ball sets here at 7PM. What time is it rising and setting in your area at this time of year? Find out sunrise and sunset times for the solstices for Honolulu and your area. From that determine A) how much longer the sun is above the horizon for each place in summer vs winter B) which place, Honolulu or your home has more sun time at each solstice? If you find that there are differences explain why they exist.